FAQ OF THE MONTH

OCTOBER 2023 

QUESTION: I am evaluating an existing metal building built in the 70s. I am trying to confirm what grade of steel was likely used for the cold-formed steel Z-purlins. Since they're 7" and 12 ga thick, I assumed they are at least 50 ksi yield strength. However, there may have been a different grade of steel available back then. I am just trying to see if that is a possibility.

ANSWER: The Metal Building Manufacturers Association has a technical publication that is intended to provide some ideas and insights into how a metal building can be retrofitted or reinforced. See page 12 for a discussion of the material properties for purlins and frames.

SEPTEMBER 2023 

QUESTION: The AISI shear provisions only seem to cover screw capacities for steel-to-steel connections. I have a condition on a project where I need to check the shear strength of screws through gypsum board and into a cold-formed steel stud. Specifically, I have a track ledger that is placed directly against a wall with (2) layers of gypsum board. The screws attach through the track ledger, through the (2) layers of 5/8" gypsum board, and into the stud flange. The track is in direct contact with the gypsum board, not the stud. The track ledger is also receiving joists. Are there published values for this type of condition? I'd like to know even if it’s just (1) layer of gypsum board. Is this even a code-accepted connection? Any insight you have will be greatly appreciated.

ANSWER: Currently the AISI Specification does not have criteria for the connection with material between the plies. Based on limited data regarding the connection behavior as illustrated by Figure 1, CFSEI Tech Note F602, Screw Connections with Other Materials or Gaps Between the Plies, was developed. The Tech Note provides design guidance regarding the evaluation of the strength of a connection.

AUGUST 2023 

QUESTION: Is there a group fastener modification factor for multiple screws or are the attached cold-formed steel members considered rigid and all of the fasteners are considered equally loaded?

ANSWER: The equations in AISI S100 Section J4 are based on tests results. The assumption made when the test results were evaluated was that all of the screws shared the load equally.

JULY 2023 

QUESTION: I am designing a parapet wall for a new project. I need help with the connection of a 362S162-54.

ANSWER: AISI D110-16, Cold-Formed Steel Framing Design Guide, offers some discussion regarding parapet walls. The discussion begins on PDF page 113. AISI D110 may be purchased at American Iron and Steel Institute Store.